1. Field of the Invention
The present invention relates generally to engines/turbines and, more specifically, to engine/turbine energy recovery.
2. Description of the Related Art
Large “off-road” diesel engines may be notoriously loud and inefficient. They may convert approximately 40% of available energy in the form of combusted fuel into effective work (or electric power if a generator set is coupled to the engine). Approximately 60% of the energy produced may be waste heat that is either rejected indirectly to the atmosphere via cooling water/air systems or directly released into the environment in the form of hot exhaust (approximately 300-450° C. depending on type of fuel burned). The hot exhaust contributes to thermal, toxic, acidic, and noise pollution.
Catalytic reactors may use ammonia to reduce emissions from diesel engines. In order for ammonia to mix properly in the exhaust stream prior to entering a selective catalytic reduction reactor it may be vaporized. Traditional systems that have injected cool liquid ammonia directly into the hot exhaust stream have encountered plugging of nozzle orifices due to the formation of ammonia bisulfate, a sticky salt substance. The evaporation of ammonia may induce a cooling effect that allows sulfur in the exhaust gas to react with the ammonia to form ammonia sulfate (NH4)2SO4 and ammonia bisulfate NH4HSO4. In order to solve this problem, additional equipment may be added (heaters, tanks, demister pads, etc.) to vaporize ammonia prior to injection. Other systems may re-circulate a hot exhaust slip stream directly into the ammonia system to provide a direct source of vaporization, however, this may create a hazardous combustion condition depending upon the concentration of ammonia being injected.
In traditional large-scale waste heat recovery processes (500 MW +) steam is typically generated for process use or to turn a turbine to produce power. Such bottoming cycles can have relatively high exhaust temperatures and typically are not cooled below acid dew points in order to avoid corrosive formation of sulfuric acid, H2SO4. Unfortunately high concentrations of acidic vapor are released into the atmosphere where eventual cooling and condensation leads to acid rain, a human health hazard and destructive property problem as well.
Because large “off road” diesel engines combust large amounts of fuel, it may be beneficial to reduce the inlet temperature of the combustion air to improve overall efficiency and performance. Traditional systems may use cooling water from cooling towers for gas turbine applications where either evaporative cooling, high pressure fogging, or refrigeration methods are employed.